A conventional air bag device is provided on a steering wheel of an automobile. This air bag device comprises an air bag having a flat bag-like configuration, a cover body for covering the air bag, and an inflator for injecting gas. The air bag is folded into a small size and is housed in the inside of the cover body by a predetermined method. The air bag device injects gas from the inflator when the sensor detects an impact of a collision in order to inflate the air bag. The cover body must be broken with the inflation pressure of the air bag, allowing the air bag to be inflated and deployed toward the driver to minimize the force of impact on the driver.
The conventional air bag is folded from the unfolded, plate-like configuration along straight lines at predetermined positions into a rectangular configuration which can be housed in the cover body. However, considerable manpower is required since it is difficult to mechanize the folding device. Therefore, it is also difficult to improve productivity.
Japanese Patent Application No. 2000-502637 discloses a device for folding an air bag that may be automated. This folding device comprises folding plates that are arranged in concentric circles or in a spiral configuration and are located opposite to the upper and lower parts of the air bag. The air bag device is inflated while it is sandwiched by the folding plates. Each of the folding plates, which are arranged in concentric circles, are moved or deformed to decrease the diameter of the concentric circles in order to fold the air bag. However, the folding device is complicated and is costly to use.
Furthermore, an air bag that is circular as seen from a planar perspective is subject to petal folding in which the air bag is gathered toward its center from its outer circumference and takes on a pleat-like configuration. Other structures are disclosed in Japanese Unexamined Patent Publication No. HEI 10-129381 and Japanese Unexamined Patent Publication No. HEI 10-217894.
The present invention provides a method for folding an air bag that provides desired folding characteristics and can decrease manufacturing costs, an air bag device, and an air bag.